1. Field of the Invention
The present invention relates to a feature extraction apparatus, a feature extraction method, an image processing apparatus, and a computer program product therefor.
2. Description of the Related Art
Techniques for extracting features from an image so as to recognize an object or the like have conventionally been known. For example, according to the feature area extraction method and the like described in Japanese Patent No. 3247305 (hereinafter, “Patent Document 1”), mutual correlations of gray-level values are calculated among mutually different images so that it is possible to extract a feature area by calculating a distribution of the mutual correlation values. As another example, a document (hereinafter, “Non-Patent Document 1”) by Rami Rautkorpi and Jukka Iivarinen, “A Novel Shape Feature for Image Classification and Retrieval”, in Proceedings of the International Conference on Image Analysis and Recognition, Lecture Notes in Computer Science (LNCS) 3211, Part I, pages 753-760, Porto, Portugal, Sep. 29 to Oct. 1, 2004 describes a technique for extracting features that are robust even in changes such as ones caused by illuminations, by using a co-occurrence matrix of intensity gradient directions. Further, Non-Patent Document 1 describes that this technique can be used for extracting features that are effective in texture classification. In this example, the co-occurrence matrix is a type of co-occurrence histogram.
To detect or recognize a specific target object, it is desirable to utilize information among mutually different images; however, the purpose of the technique disclosed in Patent Document 1 is to extract a feature area, although information among the mutually different images is taken into account. Thus, when this technique is used for object recognition, a problem arises where the level of performance is low because the technique is not intended for object recognition. Further, the technique disclosed in Non-Patent Document 1 uses a single image as a target. Thus, this technique does not take into account dealing with a plurality of images, such as images that change over time (e.g., images of walking motion).